The invention relates to a method and a circuit arrangement for linearizing nonlinear curves with a linearization circuit, wherein the curve represents the relationship between input signals and output signals of a component, in particular a sensor, and wherein an output signal is associated with each input signal.
Methods and circuits for linearizing nonlinear curves have been known in practical operation for a long time, because components frequently supply no linear relationship between the input signal and the output signal. This applies in particular to sensors, in which a nonlinear connection exists in general between the physical quantity being measured, i.e., the input signal of the sensor, and the change of the electrical signal, which the sensor in use for the measurement supplies as an output signal. In most cases, nonlinear, constantly rising or constantly decaying signals, normally voltages and/or currents develop above the measured value.
The potentials of existing A/D converters—analog-digital converters—and of D/A converters—digital-analog converters—and the use of microprocessors permit a relatively simple, mathematical linearization of curves, when the curve shape is exactly known. As an alternative thereto, it is also possible to use a microprocessor for performing a mathematical linearization with few reference values and a given basic formula.
However, these methods are problematic in that noticeable limitations exist with respect to the resolution and the speed of the linearization. If the curve is strongly bent, it will require a correspondingly high resolution of the A/D converter. Precision A/D converters of this type with a resolution of more than 16 bits are relatively expensive. Furthermore, the price of such precision A/D converters considerably increases along with the processing speed of the A/D converter. If a signal with a resolution of 17 bits or higher is to be processed with a simultaneously high signal frequency, i.e., as high as 200 kHz and higher, currently available A/D converters will make this possible at extremely high costs or in part not at all.
As an alternative, it has been common for a long time to linearize with analog linearization circuits, since analog components permit realizing a high resolution and accuracy at a high processing speed at the same time. However, this method is problematic in that the adjustment of the linearization circuit requires an accurate adjustment of the operating points of the linearization circuit, which is possible only by a manual, iterative adjustment, i.e., by often repeatedly inputting different input signals that are distributed over the measuring range, with respectively combined adjustments of potentiometers for the zero point, the amplification, and the smallest linearity deviation of the linearized curve. This procedure may take a very long time, in particular for unskilled and inexperienced operators, and may even fail in the event of a wrong manipulation. In addition, it is possible only with difficulties, or in part not possible at all to adjust over and over again exactly the same physical input signals in each adjustment step, for example, the distance of a sensor from an object of measurement. As a result, the required amount of adjustments increases accordingly to a great extent.
It is therefore an object of the present invention to provide a method as well as a circuit of the initially described type for linearizing nonlinear curves, which permit a simple and cost-favorable linearization.